This invention relates to a binder system employing polyhydroxyl compounds, glyoxal and catalyst in aqueous medium. More particularly, this invention relates to use of a catalyst which controls the reaction between polyhydroxyl compounds and glyoxal allowing new uses with heretofore unattainable versatility. Particularly the invention relates to the use of polyhydroxyl compounds comprising the saccharides and polymers made up essentially of repeating saccharide units, the amylaceous materials and hydrolysis products thereof exemplifying this latter group. This binder system has shown good utility as a foundry core binder.
The crosslinking of polyhydroxyl compounds, particularly polysaccharides like starch, with multifunctional reagents reactive with hydroxyl groups is well known and widely used. Common reagents used to crosslink starch (amylaceous materials) are formaldehyde, glyoxal, polyisocyanates, polyaldehyde resins, phenolic resins, urea formaldehyde resins and inorganic reagents including borates, phosphates, stannates and antimonates. All of these reagents have been used to crosslink cereal derived products for specific uses. When using glyoxal, the reaction proceeds so rapidly that utility of the binder system is greatly reduced. Some applications, such as foundry sand core manufacture, are difficult since the reaction takes place before the sand-binder mix can be formed into cores. This rapid reaction means that very short mixing and forming times must be employed. For making cores using the more conventional equipment such as hot box or baking type cores, a longer working life of the sand mix is required but yet the mixture must set and react rapidly with the application of heat.
Applicants are aware of no prior art pertaining to the control of the reaction rate of polyols and polyaldehydes in an aqueous medium using alkali halides. Reference has been found to the use of base acids and organic acids. U.S. Pat. Nos. 2,867,615 to Lehmann and Gandon and 2,999,032 to Dekker show reactions between glyoxal and starch in water in the presence of acids. Rumberger U.S. Pat. No. 3,293,057 discloses the reaction of starch, urea and a poly functional aldehyde. In order to maintain acid conditions, acids or acid salts are utilized. Nickerson and Weymouth U.S. Pat. No. 3,700,611 discloses the use of glyoxal, polyvinyl alcohol and cis 1,2 polyols or 1,3 polyols. No catalyst is used or mentioned. Williams and Cosica U.S. Pat. No. 3,597,313 relates to cyanamide modification of polyvinyl alcohol and subsequent crosslinking with glyoxal. These products are cationic. Other U.S. Pat. Nos. disclosing aldehydes or other crosslinking materials used with specific starch derivatives, mainly cationic starches, include: 3,051,691; 3,238,193; 3,127,393; 3,275,576; 3,135,738; 3,277,025. None of these relate to catalysis.
No prior art for a foundry binder has been located which is based on starch and polyaldehyde or on polyol and polyaldehyde. Patents disclosing starch products, some for use as foundry binders, include U.S. Pat. Nos. 2,894,859 to Wimmer and Meindl; 2,159,505 to Brugess and Johnson; 3,251,702 to Stickley et al; and 3,565,651 to Waggle. None of these patents are pertinent to the novel features of the present invention.
Foundry binders currently used in hot box and baked core making operations are thermosetting resins like phenolics, furans, urea formaldehyde and mixtures of these and oxidizable oils commonly called core oils in the industry. These binders have the disadvantage of emitting odorous fumes during the application of heat, and if the cores are to be baked, green strength additives must be used so that the cores have sufficient strength to be put into and through an oven.
The use of the catalyzed glyoxal saccharide system is applicable to foundry sand cores, cellulose press formed products, adhesives, coating binders and in many other areas. This wide utility is possible in part to the great variation in working and final properties available by controlling the amounts of reactants and catalyst and by selecting the saccharide from the wide range of materials available. A particular group of materials derived from cereal grains has been found to be uniquely beneficial in the foundry core making operation. This group is characterized by being gelatinized and of low molecular weight in comparison to native cereal or heretofore available cereal foundry binder products. An unexpectedly beneficial process to make these products is described, said process consisting of the key steps of depolymerization followed by gelatinization.